In a bombshell development, Manhattan DA Cyrus Vance Jr. is accusing the state Independence Party of complicity in the theft of $1.1 million from Mayor Bloomberg, and the DA has frozen all party bank accounts in preparation for seizing its assets.

The stunning move was disclosed in court papers Vance’s office filed this month in Manhattan Supreme Court that described the party as a “noncriminal defendant” that helped political operative John Haggerty steal Bloomberg’s campaign cash late in the 2009 mayoral race.

“There is ample evidence to believe all of the defendants made attempts to hide the evidence of the crimes and conceal the fact that the funds contributed by the mayor had not been used as originally intended,” the DA’s Office asserted.

As The Post first reported, Bloomberg contributed $1.2 million to the Independence Party in late 2009, of which $1.1 million was supposed to go to Haggerty to mount an Election Day poll-watching operation through a hastily formed company named Special Election Operations LLC.

The DA’s Office uncovered e-mails that it said demonstrated Haggerty and party Vice Chairman Tom Connolly were in cover-up mode about their unusual arrangement after Chairman Frank MacKay spoke to The Post before consulting either of them.

“This dude from the Post already got to Frank before we could speak,” Connolly notified Haggerty in an e-mail on Jan. 22, 2010, according to court documents.

“He told him the donations were very generous, but he also told him the payout was to a ballot security company to being poll watchers, lawyers, etc. for election day. This is just to keep our stories straight.”

Haggerty was none too happy to hear that.

“How could that happen? I sent the quote last week!!!” he responded minutes later.

Haggerty, once a close campaign aide to Bloomberg, is now facing criminal charges in a case that has riveted the city’s political community.

According to the court papers, Connolly and Haggerty also fabricated a written contract to make it appear the party had contracted with Haggerty to conduct the Election Day operation.

“Because SEO [Special Elections Operations] did not exist before Dec. 3, 2009, after the election had passed, the document was apparently backdated to make it look like it had been executed on Oct. 15, 2009, before the election,” the DA reported.

On another occasion, the court papers allege, Connolly tried to conceal from the Board of Elections a transfer of the mayor’s funds to Haggerty.

“A party representative has made it clear in testimony that Connolly directed these payments to Haggerty and stated they did not need to be reported,” the DA said.

The Independence Party is the third largest in the state, which is why Vance said he waited to act so as not to interfere with state elections last November.

MacKay called The Post last night to say he can’t wait to tell the party’s side of the story at a show-cause hearing on March 8 before Manhattan Supreme Court Judge Martin Shulman.

“We received a $1.2 million donation, which somehow retroactively became a $100,000 donation, and we very much look forward to an evidentiary hearing,” MacKay said.

Dennis Lemke, one of the party’s lawyers, denied that the party knew of Haggerty’s alleged million-dollar scam.

“There’s no in any way aiding, abetting or any collusion,” Lemke said.

He said the party was prepared to return any of the mayor’s remaining funds — but only to the mayor.

“They’re not seeking money for Bloomberg,” he said of the DA’s Office. “They’re seeking it for themselves.”